ZnO 0001 Zn terminated with passivation- no gap found

[nicholas_dimakis1]

Hello

I am trying to calculate the band gap for ZnO 0001 (Zn terminated surface) using the poscar below

1.00000000000000
3.3010279642712312 0.0000433829919160 -0.0000045345237691
-1.6504762632064913 2.8587956792990439 0.0000051446633796
-0.0000582528888118 0.0000337046777105 35.0466728686164757
Zn/501fddbd827 O/818f92134a0a H.5/333a5f69c2
7 7 1
Selective dynamics
Direct
0.6666666259993619 0.3333333139043901 0.3596064239709165 F F F
0.6666666259993619 0.3333333139043901 0.5090002440822161 F F F
0.6666730754626056 0.3333268644592838 0.6573185415055889 T T T
0.3333364233663329 0.6666635167689995 0.7306780347498141 T T T
0.3333332840173497 0.6666666560348489 0.2840068403627782 F F F
0.3333332840173497 0.6666666560348489 0.4343635163817581 F F F
0.3333332840173497 0.6666666560348489 0.5834163620524393 F F F
0.6666674012626553 0.3333325387308155 0.2668813230001900 T T T
0.6666666259993619 0.3333333139043901 0.4170077826760732 F F F
0.6666666259993619 0.3333333139043901 0.5654158560343561 F F F
0.6666663590577196 0.3333335807657876 0.7177949273069295 T T T
0.3333332840173497 0.6666666560348489 0.3439494087212722 F F F
0.3333332840173497 0.6666666560348489 0.4910945190104457 F F F
0.3333290943147162 0.6666708457332049 0.6420286930114597 T T T
0.6666699913861704 0.3333300086185594 0.2368484010855669 F F T

Hydrogen passivates the O atom at the bottom of the slab, as shown in https://link.springer.com/article/10.10 ... 007-9561-5 and http://www.jos.ac.cn/fileBDTXB/oldPDF/09120802.pdf. Passivation is also explained at https://journals.aps.org/prb/abstract/1 ... .68.245409.

I tried different H atom charges but still did not get a band gap. I must say that for the O-terminated 0001 surfaces, whereatoms passivate Zn atoms and H the band gap is found.

Thanks-Nick

[henrique_miranda]

Could you elaborate a little bit more, what is the question?
You would expect to get a bandgap, but you don't?

[nicholas_dimakis1]

Hello

As shown in the links from past work, the band gap should be between -1 and -2 eVs.

Thanks-Nick

[henrique_miranda]

I have to apologize, but I still don't understand what is the question.
Could you please share a little bit more details about your calculation, the results you obtain and what you would expect according to what paper exactly?

[nicholas_dimakis1]

Hello

ZnO 0001, terminated at the Zn surface, must show a bandgap at about -1 eV to -2 eV from the Fermi energy if the oxygen atoms on the other surface of the slab are passivated with H atoms. If no passivation occurs, then no band gap will be observed. However, in my calculations, I passivate the O atom on the other surface with an H atom, and no band gap is observed. I tried various charges for the H atoms, but it still did not work.

However, for the ZnO 0001, terminated at the O surface, where the Zn atoms on the other surface are passivated with H atoms (as H1.5), the band gap at the Fermi energy is observed as expected.

The ZnO 0001 must show different bandgaps if the surface is terminated with Zn atoms than with O atoms, which agrees with past reports.

Therefore, in my calculations, a bandgap is observed only when Zn atoms are passivated, whereas when the O atoms are passivated, the ZnO appears metallic (which is incorrect).

I included the data for ZnO 0001, terminated at the Zn surface only.

Thanks for your help-Nick

[henrique_miranda]

Thank you for the clarification. I think I understand the question now.
Did you perform an ionic minimization?

[nicholas_dimakis1]

Yes, a partial optimization was performed. See POSCAR file below

1.00000000000000
3.3010279642712312 0.0000433829919160 -0.0000045345237691
-1.6504762632064913 2.8587956792990439 0.0000051446633796
-0.0000582528888118 0.0000337046777105 35.0466728686164757
Zn/501fddbd827 O/818f92134a0a H.5/333a5f69c2
7 7 1
Selective dynamics
Direct
0.6666666259993619 0.3333333139043901 0.3596064239709165 F F F
0.6666666259993619 0.3333333139043901 0.5090002440822161 F F F
0.6666730754626056 0.3333268644592838 0.6573185415055889 T T T
0.3333364233663329 0.6666635167689995 0.7306780347498141 T T T
0.3333332840173497 0.6666666560348489 0.2840068403627782 F F F
0.3333332840173497 0.6666666560348489 0.4343635163817581 F F F
0.3333332840173497 0.6666666560348489 0.5834163620524393 F F F
0.6666674012626553 0.3333325387308155 0.2668813230001900 T T T
0.6666666259993619 0.3333333139043901 0.4170077826760732 F F F
0.6666666259993619 0.3333333139043901 0.5654158560343561 F F F
0.6666663590577196 0.3333335807657876 0.7177949273069295 T T T
0.3333332840173497 0.6666666560348489 0.3439494087212722 F F F
0.3333332840173497 0.6666666560348489 0.4910945190104457 F F F
0.3333290943147162 0.6666708457332049 0.6420286930114597 T T T
0.6666699913861704 0.3333300086185594 0.2368484010855669 F F T

The problem is that dangling bonds still exist when O is passivated by H (ZnO 0001 Zn terminated). However, when Zn is passivated with H atoms, the dangling bonds are minimized, and the gap appears in the band structure (ZnO 0001 O terminated).

The H atoms cannot move in the x and y planes during geometry optimization.

Thanks.